This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Overview: In a broad sense, my laboratory is interested in identifying and understanding factors that affect the health of marine mammals. Much of our recent research efforts have focused on the effects of stress on the health and function of cetaceans. Factoring centrally into this work is an interest in the potential link between environmental contaminants and stress in cetaceans. The work proposed here will help define how stress may affect particular organs within an animal and thus it represents an important initial step in efforts to address the link between contaminants, stress, and cetacean health. Specific Objectives: 1. Characterize the normal histological features of the conduction system of the heart in T. truncatus. 2. Examine the conduction system in stranded T. truncatus for evidence of catecholamine-induced injury such as contraction band necrosis. General Approach: Standard techniques will be followed for correlating the gross anatomy with the microscopic topography of intracardiac structures. Next, histology and when tissue preservation is sufficient, transmission electron microscopy, will be used to characterize the cellular features of the cardiac conduction system. Finally, we will use histology and when feasible, electron microscopy, to probe for evidence of cell/tissue changes consistent with catecholamine-induced injury. These degenerative changes have been well characterized in various species (Haft, 1974;Windingstad et al., 1983;Turnbull and Cowan, 1998).